9v Battery Indicator

[AngelLaHash]

Forward Current 20mA

Forward Voltage (V)
RED: Typical: 2 V Max: 2.4V
GREEN: Typical: 3.4 V Max: 3.8V
BLUE: Typical: 3.4 V Max: 3.8V

I plan to use Red/Green for the Battery and the Blue with a 9v Supply hooked up to a SPDT Relay so save the Battery

As from this LED the Red needs far less voltage and not as much MAX
also i dont know what Levels i should set it to know the Battery is becoming usless
Dont want to use any Chips

 

[MrAl]

Hello,

Did you try using comparators yet? Yes that is 'chips' but it will work much better.

 

[AngelLaHash]

I wanted to Limit the amount drain on the battery

Ive just brought about 100 of tri-led Red/Blue/Green as a Battery Test/Mains
What i wanted to use on a Active Guitar/Guitar Effects

I guess i could say BLUE is Battery GOING
RED Battery and Green Mains
-----
Just looking at the circuit, its using the Transistor as a Drain away from the RED LED

So if change the 470Ohms to 270Ohms
And I'm guessing the 1K feeding the RED LED should be changed to say 300Ohms

Im not sure about the Transistor BC547 (if looking a the 470/1000 as a PD then would be 0.47

 

[MikeMl]

Is this for a 9V battery?

Is so, the indicator is likely to draw more power from the battery than the actual circuit being powered by the battery

You would be better served by having no indication while the battery is ok, and then flashing an ultra-bright Led when the battery is about to be exhausted.

 

[AngelLaHash]

Good point Mike..
The reason i wanted a light for when the battery was on, because people forget and leave it on. (would a light matter in that case)
the Flashing i like the idea of, less power used but still pushes a point

 

[MrAl]

Hello,

Yes flashing an ultrabright LED can be used anytime. You can keep the current low and only flash once in a while. If you flash once every 10 minutes, the battery will last pretty long if you also keep the current low.

This is starting to scream microcontroller chip
With the low power sleep function uC chips you can keep running for a year flashing once every 10 minutes.

 

[MikeMl]

Good point Mike..
The reason i wanted a light for when the battery was on, because people forget and leave it on. (would a light matter in that case)
the Flashing i like the idea of, less power used but still pushes a point

Sounds like you might want to use two leds, one to indicate that it is turned on, and another (different color) to indicate that it is on, but the battery is beginning to fail.

If this is for an audio device, possibly the transient current draw during the on-cycle of the LED flash might introduce a "click" into the audio output?

Check out the LEDs that have a built-in flasher.

I have an extremely low-power LED flasher circuit, somewhere.

Also, you might want to read this previous thread to get some ideas.